#include <stdio.h>

int main(){
	
	int number = 0;
	int sum = 0;
	int count = 0;
	
	scanf("%d", &number);
	while(number > 0){
		sum += number;
		count ++;
		scanf("%d", &number);
	}
	
	printf("%f", 1.0*sum/count);
	
	return 0;
}
